Hydraulic master cylinder



Oct. 3o, 1962 J. w. DAVIS 3,060,691

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Oct. 3o, 1962 J. w. DAVIS 3,060,691

HYDRAULIC MASTER CYLINDER Filed April 25, 1961 2 Sheets-Sheet 2 United States Patent Olitice 3,060,691 Patented Oct. 30, 1962 3,060,691 HYDRAULIC MASTER CYLINDER John Walter Davis, Birmingham, England, assignor to Girling Limited, Birmingham, England, a British com- Pauy Filed Apr. 25, 1961, Ser. No. 105,392 5 Claims. (Cl. 60-54.6)

This invention relates to improvements in master cylinders for hydraulic systems such as hydraulic braking systems for vehicles.

Our invention is particularly concerned with master cylinders of the type incorporating a main piston and a floating piston adapted to `apply pressure to liquid in separate pressure spaces or working chambers which are connected to separate systems or parts of a system or systems, such as the brakes on the vfront and rear wheels of a vehicle, and which Vare in communication with a liquid reservoir or reservoirs through suitably arranged passage ways when the pistons are in their fully retracted positions.

According .to our invention, in a master cylinder of the type set forth, communication between the pressure spaces and the reservoir or reservoirs is controlled by movement of one of the pistons.

The cylinder can be so arranged that communication between the pressure spaces and the reservoir or reservoirs is cut off simultaneously and the travel of the input or main piston necessary to produce pressure in the system or systems is reduced `to a minimum.

The establishment Iand cutting-oli of communication between the pressure spaces and the reservoir or reservoirs will normally be controlled by valve means.

The valves may be coupled or interconnected so that the opening or unseating of one valve by a piston simultaneously opens or unseats the other valve, or both valves may be actu-ated by either the main or the floating piston.

When the valves are opened or unseated separately by the two pistons, and a pedal or the like, by which the main piston is actuated, is released, the return movement of the floating piston may be delayed by lthe diierential pressure in the working space between the pistons, and by arranging for the recuperation valve communicating with this space to open the other recuperation valve when it is itself opened by the main piston, the pressure in both working spaces will be relieved simultaneously.

Similarly, when the main piston is advanced to apply the brake, both recuperation valves will close simultaneously and pressure will build up simultaneously in both working spaces.

Where the two valves are coupled or interconnected, the recuperation valve which is actuated by the other, which is controlled by a piston, may be located at any convenient point between the liquid reservoir and the working space with which it communicates.

Where the two valves are both opened or unseated by one of the pistons, they may be engaged simultaneously by abutments located adjacent to opposite ends of the piston.

Two practical forms of master cylinder embodying our invention are Iillustrated by way of example in the accompanying drawings in which:

FIGURE 1 is a longitudinal section in a vertical plane of one form of master cylinder; and

lFIGURE 2 is a similar section of a modiiied master cylinder incorporating coupled recuperation valves.

The master cylinder illustrated in FIGURE l is intended for use in an hydraulic braking system. It cornprises a main body part having a bore v11 in which works a main piston 12 which is adapted to enter an axially aligned chamber 13, a stationary seal 14 for the piston being located in the chamber Aat the inner end of the cylinder. The piston is actuated by a thrust rod 15 which enter-s an axial recess in the outer end of the piston and the outer end of which is coupled by any convenient means to a pedal. When the pedal is released, the piston is retracted by a spring 16.

A second body part 17 secured by bolts 18 to the main body part has a cylindrical bore 19 in axial alignment with the bore 11. A sealed joint is made between the two body parts by a spigot on the part 17 entering a counterbore at the forward end of the chamber 13, a sealing ring 21 being located in an annular groove in the spigot.

A oating piston 22 working in the bore 19 has on its forward end a reduced extension 23 terminating in a radially extending ange 24. The main part of the piston is formed with a longitudinal axial lrecess into which enters a head 25 on the forward end of a reduced extension 26 of the main piston 12. A compression spring 27 is located between the inner end of the recess and a radial shoulder 28 on the rear end of the head 2S to urge the pistons apart, their separation being limited by a U-shaped clip 429 which tits into opposed slots 31 in the piston 22 and provides an abutment -for the rear end of the head 25. At its rear end the oating piston 22 has a radially projecting flange 32, which in the fully retracted position of the piston shown in the drawing abuts against an internal annular shoulder 33 in a skeleton liner 34 located in the chamber 13 and serving as a retainer for the seal 14.

Communication between the chamber 13 and a lluid reservoir 39 is controlled by a valve 41 mounted in a valve body 42 screwed into the upper end of a passage 43 extending from the chamber into the reservoir. The valve is biassed towards the closed position by a spring 44 and has a stem 45 projecting inwardly into the path of the ange 32 on the rear end of the piston 22.

Communication between the pressure space 36 in front of the floating piston 22 and a reservoir 46 is controlled by a similar valve to which the same references have been applied, the stem of this valve projecting inwardly into the path of the flange 24 on the forward end of the piston 22.

The positions and spacing of the valves are such that as the piston 22 returns to its fully retracted position on release of the brake, the stems of the valves are engaged by the flanges 32 and 24 on the piston and the valves are tilted simultaneously to move them away from their seatings and to establish free communication between the reservoirs and the pressure spaces in the cylinder.

When the main piston 12 is advanced to apply the brake, the oating piston 22 moves with it, and as the piston 22 moves forwardly, both valves close simultaneously and pressure builds up simultaneously in the two pressure spaces.

In the alternative construction shown in FIGURE 2, the body 51 has a single straight-through bore closed at its forward end by a plug 52. The main piston 53, which is actuated by a pedal through a thrust rod 54, works in the rear end of the cylinder bore and is litted with a cup seal 55.

The oating piston 56 is sealed by an annular seal 57 located in an annular groove in the piston. A return spring 58 is located between the forward end of the piston 56 and the plug `52, and on the rear end of the piston there is a radially projecting flange 59. A rod 6.1 is carried by a disc 62 located in a recess in the rear end of the piston 56 and passes through an axial hole in the end of a cupshaped pressing 63 located in a complementary recess in the main piston 53, the rear end of the rod 61 having a head of greater diameter than the hole in the pressing. A compression spring 65 located between the pistons abuts at one end on the disc 62 and at the other end on a radial ange on the pressing 63.

A reservoir 66 is integral with the body of the master cylinder and is divided into two by a partition 67. Communication between the pressure space between the piston and the reservoir on one side of the partition is controlled by a valve 68 similar to the valves described above, this valve having a stem 69 projecting into the path of the ange 59 on the oating piston, Communication between the reservoir on the other side of the partition and the pressure space in front of the floating piston is controlled by a similar valve 71 but this valve has no inwardly projecting stem.

The stems of both valves however are extended away from the cylinder into the reservoir and their extremities are positively coupled by a link 72 located above the partition 67 so that both valves are unseated simultaneously when the inwardly projecting stem 69 of the valve 63 is engaged by the ange 59 on the floating piston, both valves closing simultaneously when the piston moves forwardly in the application of the brake.

I claim:

1. A master cylinder for an hydraulic system comprising a cylinder, a positively actuated main piston working in said cylinder, a oating piston working in said cylinder, separate spaces between said pistons and between the iloating piston and one end of the cylinder respectively, a reservoir for working uid, passages connecting said pressure spaces to said reservoir, and separate valves controlling said passages actuated simultaneously by one of said pistons.

2. A master cylinder for an hydraulic system comprising a cylinder, a positively actuated main piston working in said cylinder, a floating piston working in said cylinder, separate pressure spaces between said pistons and between the floating piston and one end of the cylinder respectively, a reservoir for working uid adjacent to said cylinder, ports in the cylinder wall providing communication between said pressure spaces and the reservoir, and valves controlling said ports and actuated simultaneously by one of said pistons.

3. A master cylinder as in claim 2 wherein said valves are coupled together whereby actuation of one valve by one of the pistons causes simultaneous actuation of both valves.

4. A master cylinder as in claim 2 wherein said valves are spring-biased to the closed position and are unseated by the engagement with portions of the valves of abutments on opposite ends of the floating piston when said piston is in its retracted position.

5. A master cylinder as in claim 2 wherein said ports in the cylinder wall provide communications between the pressure spaces and separate reservoirs.

References Cited in the le of this patent UNITED STATES PATENTS 2,332,301 Cox Oct. 19, 1943 FOREIGN PATENTS 819,786 Germany Nov. 5, 1951 

